As compared to other display devices such as liquid crystal display (LCD) devices, the organic light emitting diode (OLED) display devices are self-emitting apparatuses that do not require a backlight. Having the advantages of fast response, a wider viewing angle, high brightness, more vivid color rendering, thinner and lighter, they have found a wide range of applications in display field.
Typically, a convention OLED includes an anode, a light emitting layer and a cathode. The light emitting layer often includes a light emitting layer (EML), and optionally one or more of a hole injection layer (HIL), a hole transport layer (HTL), an electron transport layer (ETL), and an electrode injection layer (EIL). When a voltage is applied between the cathode and the anode, charge carriers (electrons and holes) are injected from the cathode and the anode into the emitting layer. The electrons and holes are recombined in the emitting layer, which emits light.